Engineers with niche knowledge

Given all of the new emergency preparedness requirements on nursing facilities, I am confident that many of us will have to alter our EES at a minimum and potentially add or replace generators.

We have an Electrical Engineer we've used for over a decade on new construction and is great for the easy Type II EES design on a new nursing facility. However, we need to look elsewhere once we start diving into modifications to older systems, especially as it relates to all of the new requirements and all of the re-wiring/design that potentially has to take place. I need someone who has been there and done that.

What is the best way to locate someone with niche experience like this? I'd appreciate any guidance.